Improved optical system for a single lens reflex camera

ABSTRACT

A single lens reflex camera in which an external scale for adjusting the focus or shutter of a camera is visible with the object image in a viewfinder. Between the scale and a viewfinder there are provided a pentagonal prism and a convergent lens for forming a real image of the scale at the viewfinder eyepiece.

O Umted States Patent 1151 3,675,558 Kuramoto et al. [451 July 1 l, 1972[54] OPTICAL SYSTEM FOR A SINGLE LENS [561 Relerences Cited REFLEXCAMERA UNITED STATES PATENTS 1 1 lnvenwfir Ywhio Xvi-1mm, Sakai-511i;5mm 3.174.416 3/l965 Heer Klotz 1.95/44 R g k k z ihi. both of Japan3,250.196 5/1966 011 et a] ..95/44 R [73] Assignee: Mlnolla CameraKabushlld Kaisha, Osaka, RE N PATENT OR APPLICATIONS Japan 593,2675/1959 Italy............................... .......9S/IlV 936,964 9/1963Great Britain .....95/l1 V [22] Flled: Oct. 10, 1969 I PrimaryExaminerSamuel S. Matthews 1 App. 86S453 Assistant Examiner-E. M. BeroAttorney-Watson, Cole, Grindle & Watson [30] Fore n A cation PriorltData is y 511 ABSTRACT O t. 19, I968 J c apan 3/9139 A single lensreflex camera In whlch an external scale for adjusting the focus orshutter of a camera is visible with the oh- 52 us. 01 ..95/42, 95/1 1 v,95/44 R ject image in a viewfinden Beween the scale and a viewfinder [5l Int. Cl. 1 4 1 .G03b [9/ [2 there are provided a pentagonal Prism d aconvergent |en5 [58] Field Of SCII'CII ..95/l l V, 42, 44 for forming areal image 0f the scale at the viewfinder eyepiece.

2 Claims, 5 Drawing Figures PKTENTEnJuL 11 m2 3.675.558 sum 1 BF 2 FIG.2

PRIOR ART Ma/$ M ava; 14

BACKGROUND OF THE INVENTION In a single lens reflex camera, wherein theexposure adjustment scales such as the diaphragm scale, shutter speedscale,

etc. as well as objective images are visible in a viewfinder and thecamera operator, while looking through the viewfinder, can focus theobjective for an object and view, the exposure adjustment scales on anexposure setting member such as a diaphragm setting ring or shutterspeed setting ring into the viewfinder. However, as compared with anarrangement provided with a separate scale, such an arrangement has noneed of an interlocking mechanism for both scales or operationalmechanism for the other scale, so that it is advantageous in simplifyingthe structure of the camera. In the arrangement in the prior art such asshown in FIG. 1 the optical path length of the scale image and theobjective image are not equal to each other, so that the visibilityadjustment of the scale and object image is difficult.

SUMMARY OF THE INVENTION The present invention relates to a single lensreflex camera, and more particularly to an improvement in a device forviewing the exposure setting scale in the viewfinder using a pentagonalprism and is characterized in that the exposure adjusting scalesgraduated on an exposure adjusting member are projected into thepentagonal prism and an optical system for forming images is disposed inthe path of the incident light rays so as to allow real images of thescales to form images from the eyepiece approximately equal to theoptical path length from the focusing plate to the eyepiece.

The primary object of the present invention is to provide a single lensreflex camera in which the optical path length in a viewfinder opticalsystem of the exposure element scale image is approximately equal to theoptical path length of the object image and thus when viewing theseimages through an eyepiece the visibility adjustment is easy and it ispossible to view both images clearly at the same time.

The second object of the present invention is to provide apparatus toadjust the size of image of the exposure element scale shown in thefinder through the same optical system for forming an image thereof.

The third object of the present invention is to provide a single lensreflex camera in which the visibility adjustment for the image of theframe surrounding the exposure element scale image is easy and whenviewing the finder the objective image, the exposure element scaleimage, and the frame image thereof can be viewed clearly at the sametime.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view showing anoptical system for propagating the exposure element scale in a wellknown exposure setting member in the prior art into a pentagonal prismin a single lens reflex camera.

FIG. 2 is a front view of a viewfinder field of the same well knownembodiment.

FIG. 3 is a side view showing an optical formation of an embodiment inaccordance with the present invention.

FIG. 4 is a front view of a viewfinder field of the same embodiment.

FIG. 5 is a side view showing an optical formation of another embodimentin accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG. 1, inprojecting the exposure adjusting scale on a well known exposureadjusting member in the prior art to a pentagonal prism in a single lensreflex camera, the exposure adjusting member, for example, diaphragmadjusting ring 1 turns substantially at a fixed position relative to thelens barrel projecting from a camera, so that the diaphragm scale la onring 1 is projecting to pentagonal prism 5 of the viewfinder on thecamera body through small prism 6'. The optical path length to eyepiece15 is constant, so it is difficult to change the length thereof.Further, the light rays projected from an objective lens not shown inthe drawings form an image on focusing plate 13 by means of reflector12. The image on focusing plate 13 is projected to pentagonal prism 5through condenser lens 14 and reflected by the inside surface thereof toreach eyepiece 15, so that the optical path length of the image in theviewfinder is also constant. And, from the view point of theconstruction of a camera, it is almost impossible to design so that theoptical path length between diaphragm setting ring la and eyepiece 15may be equal. For this reason, when viewing the viewfinder as far as thevisibility adjustment is not given it is impossible to see clearly thediaphragm scale image shown in FIG. 2 together with objective image [0'at the same time.

In the present invention, as shown in FIG. 3 small prism 6 is mountedonto upper side surface 5b of pentagonal prism 5 facing eyepiece l5, andto project the diaphragm scale la on diaphragm setting ring 1 passingthrough reflectors 2a and 2b from small prism 6 into pentagonal prism 5,an image forming optical system composed of concave lens 3 and convexlens 4 is disposed so as to form an image of diaphragm scale 10 onreflector 7 disposed on the front side of bottom face 5d of pentagonalprism 5 and outside thereof or on the optical axis close thereto. And,light rays from the image forming plane are projected again intopentagonal prism 5 through bottom face 5d thereof and reflected by topface 5a and further reflected by front reflection face 5c, and thenreflected from back face 5e to enter eyepiece 15. And, the optical pathlength thereof is substantially equal to the optical path length alongwhich the objective image on focusing glass 13 is projected from bottomface 5d of pentagonal prism 5 and reflected by the inside surfacesthereof, and enters eyepiece 15 through back face 52 of pentagonal prism5. In this manner, it is obvious also from the drawings that such arelation as described above can be formed very easily by selecting thefocal distance of the lens system 3-4 and the position on the opticalaxis. The above description relates to the diaphragm scale, however, itis quite the same for the shutter speed scale.

Besides, in the present invention by forming frame 8 for forming frameimage 11 surrounding the exposure adjusting scale image on reflector 7,it is possible to allow the optical path lengths formed between frame 8and the diaphragm scale image, and focusing plate 13 respectively andeyepiece 15 to coincide and accordingly possible to see clearly theseimages at the same time through eyepiece 15 as shown in FIG. 4.

In addition, according to the present invention by selecting the focaldistance of image forming lenses 3, 4 it is possible to adjust freelythe size of the exposure element scale image 90 so as to overcome anydifficulty to project the numeral values in the viewfinder field becausethe image is neither too large or small.

In the embodiment shown in FIG. 5, diaphragm scale image la is formed onthe front side of bottom face 5d of pentagonal prism 5 through imageforming lenses 3, 4, and the front side being applied with a vacuumevaporation so as to form reflection face 7'. And, in order to coincidethe optical path length for reflection plane 7 exactly the opticaldesign is subject to restrictions, however, it is easy to coincide itapproximately, and by doing so there is no necessity of providingreflector 7 so that it is favorable especially for small-sized cameras.

By the way, in both embodiments described above, it is possible to formreflectors 2a, 2!) from one prism and also possible to change imageforming lenses 3, 4 to a single lens.

What is claimed is:

1. In a single lens reflex camera including a viewfinder having afocusing plate, a pentagonal prism and an eyepiece, and an adjustablesetting member having a scale external to the viewfinder, thecombination comprising:

optical transmitting means for transmitting an image of the scale tosaid pentagonal prism,

light converging means for forming a real image of said scale throughsaid pentagonal prism at a location which is substantially the sameoptical distance from said eyepiece as the optical distance from saideyepiece to said focusing plate,

reflecting means for directing the real image of said scale to saideyepiece through said pentagonal prism, and a said reflecting means ismounted beneath the base face of said pentagonal prism.

2. in a single lens reflex camera including a viewfinder having afocusing plate, a pentagonal prism and an eyepiece, and an adjustablesetting member having a scale external to the viewfinder, thecombination comprising:

optical transmitting means for transmitting an image of the scale tosaid pentagonal prism,

light converging means for forming a real image of said scale throughsaid pentagonal prism at a location which is substantially the sameoptical distance from said eyepiece as the optical distance from saideyepiece to said focusing plate,

reflecting means for directing the real image of said scale to saideyepiece through said pentagonal prism, and

said means for reflecting is a small reflective surface formed on aportion of said base face.

1. In a single lens reflex camera including a viewfinder having afocusing plate, a pentagonal prism and an eyepiece, and an adjustablesetting member having a scale external to the viewfinder, thecombination comprising: optical transmitting means for transmitting animage of the scale to said pentagonal prism, light converging means forforming a real image of said scale through said pentagonal prism at alocation which is substantially the same optical distance from saideyepiece as the optical distance from said eyepiece to said focusingplate, reflecting means for directing the real image of said scale tosaid eyepiece through said pentagonal prism, and said reflecting meansis mounted beneath the base face of said pentagonal prism.
 2. In asingle lens reflex camera including a viewfinder having a focusingplate, a pentagonal prism and an eyepiece, and an adjustable settingmember having a scale external to the viewfinder, the combinationcomprising: optical transmitting means for transmitting an image of thescale to said pentagonal prism, light converging means for forming areal image of said scale through said pentagonal prism at a locationwhich is substantially the same optical distance from said eyepiece asthe optical distance from said eyepiece to said focusing plate,reflecting means for directing the real image of said scale to saideyepiece through said pentagonal prism, and said means for reflecting isa small reflective surface formed on a portion of said base face.